1. Field of the Invention
The present invention relates to a telecine conversion method detecting apparatus for detecting, in a movie film, whether or not an input video signal is a telecine converted video signal generated in accordance with a 2-3 pull-down method, a 2-2 pull-down method, and the like.
2. Description of the Related Background Art
Video signals of standard television systems such as the NTSC system often include video signals based on movie films. A movie film is shown at a rate of 24 frames per second, while a video signal of the standard television system is an interlaced video signal broadcast at a rate of 60 fields per second. Therefore, a movie film is converted to a telecine format based on a 2-3 pull-down method to provide a video signal compatible with the standard television system.
In the 2-3 pull-down method, first, a movie film is scanned to generate a sequentially scanned video signal having a frame frequency of 24 Hz. For example, a first frame of the movie film is converted to a first and a second field of the video signal; a second frame to a third through a fifth field; a third frame to a sixth and a seventh field; and a fourth frame to an eighth through a tenth field. The last fields (the fifth field and tenth field) in the conversion of one frame to three fields are fields having the same video contents as the first fields (the third field and eighth field).
In the 2-3 pull-down method, every two frames of a movie film, five fields of a video signal of the standard television system are formed. The frames of the movie film are converted to the video signal which alternately repeats two fields of the video signal and three fields of the video signal.
When the conversion is performed in the foregoing manner, for example, the third field and fifth field, and the eighth field and tenth field are the same video signals, respectively, so that an inter-frame difference between the fifth and tenth fields decreases. Such a relationship occurs every fifth field.
Specifically, an absolute value of an inter-frame difference is accumulated in one field period, the accumulated value is compared with a predetermined threshold value, and a motion field is determined when the accumulated value is larger than the threshold value while a still field is determined when equal to or less than the threshold value. Thus, the still field is determined every fifth field in a video signal converted in accordance with the 2-3 pull-down method. The still field is detected to discriminate an image converted in accordance with the 2-3 pull-down method from a general image.
However, the aforementioned detecting method accumulates an absolute value of an inter-frame difference for one field period and compares the accumulated value with a predetermined threshold over a plurality of fields to detect a periodic pattern of a telecine converted image, so that inter-frame difference increases, for example, if noise is included in a video signal, possibly causing the detecting method to erroneously determine a motion field, even though it is a still field.
If an input video signal is erroneously detected in regard to the telecine conversion method, the video signal is processed as a general image though it is a telecine image, resulting in a degraded quality of the displayed image.